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Why do DSLRs use a mechanical shutter?
My wife and I were in Best Buy and I was looking at the Canon 40D. (We currently have just a Canon Powershot G2). She took a couple shots with the 40D and said "hey, what's that sound?" I told here it was the mirror flipping and the shutter opening and closing. She asked me why it had a mechanical shutter, and I was stumped..

What's the reason DSLRs don't use an electronic shutter? If I understand correctly the 40D does have one for shooting "silent mode" so why not use that all the time?.

What's the advantage of the mechanical shutter? It's sure not lifespan. I've searched the net but cannot find out why DSLRs continue to use this type of shutter..

Matt..

Comments (34)

Well unless you get rid of the optical viewfinder you need the mirror in place and mirror slap is normally noisier than the shutter firing on it's own I can't help you with why mechanical shutters are necessary...

Comment #1

Pentaxiantrooper wrote:.

Well unless you get rid of the optical viewfinder you need the mirrorin place and mirror slap is normally noisier than the shutter firingon it's own.

Yeah, I understand why you need the mirror, it's the shutter that I'm getting hung up on..

Thanks...

Comment #2

The diaphragm, or F-stop, or lens opening as somme cvall it, might be considered as the diameter of the plumbing that lets the light through into the camera..

The shutter, an assembly of either vertical or horizontal blinds, determines how long the light may flow into the camera.The mirror's role is to allow you to see what you get into the picture..

Whether or not the shutter is controlled by a spring or an electric coil, it is mechanical and very delicate, although extremely precise..

All DLSR's on the market have a mechanical shutter mechanism and only the control of that mechanism may differ from one manufacturer to the other..

Now to get back to your initial question : SLR cameras have mechanical shutters because nobody has come up with anything better...

Comment #3

What if they implement electronic cut off in the sensor? will that eliminates the shutter?.

Outwest wrote:.

Pentaxiantrooper wrote:.

Well unless you get rid of the optical viewfinder you need the mirrorin place and mirror slap is normally noisier than the shutter firingon it's own.

Yeah, I understand why you need the mirror, it's the shutter that I'mgetting hung up on..

Thanks..

No hesitation when capturing moments..

Helping other is doing good for yourself, and treating the earth a little better will help the next generation.http://moments.zenfolio.com..

Comment #4

Commangor wrote:.

What if they implement electronic cut off in the sensor? will thateliminates the shutter?.

Exactly! Isn't that what the small point and shoot cameras do? They don't actually have a mechanical shutter that opens and closes do they? Why can't this be implemented on DSLRs? It would be quiter and less moving parts. There has to be a good reason but so far I can't find one...

Comment #5

Well it makes it harder to exclude all light for things like dark frame noise reduction and a shutter helps to protect the sensor from dust, otherwise you would have to put an airtight seal around the mirror to avoid picking up dust during lens swaps...

Comment #6

Pentaxiantrooper wrote:...a shutter helps to protect the sensor from.

Dust, otherwise you would have to put an airtight seal around themirror to avoid picking up dust during lens swaps..

Ok, now that makes sense...

Comment #7

Outwest wrote:.

Pentaxiantrooper wrote:...a shutter helps to protect the sensor from.

Dust, otherwise you would have to put an airtight seal around themirror to avoid picking up dust during lens swaps..

Ok, now that makes sense..

No, it doesn't. The shutter is NOT airtight. Duh....

Here are the real reasons (it's a bit long, but often that's the case with questions...they don't always have a one-line answer)..

The shutter in dSLRs do two things:.

1. Time the exposure..

2. Exclude light from the sensor during non-capture times (which is MOST of the time)..

The first one is the simpler of the two...let's start there. Yes, it would be easy to substitute an electronic shutter. However, most dSLR sensors don't have that capability at this time. And there are small issues with electronic shutters. There are many ways to do it. The cheap ways have problems.

Most P&S cameras have a rolling shutter. Quality concious dSLR buyers will not like this method..

That leaves the more expensive "global" or "frame" shutter. It is more expensive because it requires an additional transistor at each photosite. That may sound trivial, but if a normal CMOS photosite has 2 transistors, that is a 50% increase in transistors. Even worse, it increases the non-photosensitive area at each photosite by about 50%. That negatively impacts light-gathering capability and this increases noise. Then there is the patent position.

Some of these patents cover various ways to implement "global" shutters! Perhaps Japan, Inc. is simply waiting until these patents expire?.

The second reason re blocking light from the sensor is probably more germaine..

ALL cameras, even P&S types, have a "shutter" to block light from the sensor. This is required because if light is continuously shining on the sensor, all the data would have to be transferred SIMULTANEOUSLY. Most sensors transfer data serially. To keep the photosites from continuing to accumulate photons, cameras close the shutter during the period when data is being transfered. A sensor with a "global" electronic shutter helps, but all Silicon areas that are un-masked generate electrons when photons hit them. These "free" electrons can decrease the signal-to-noise ratio..

SO, for several reasons, manufacturers must have a shutter. In a P&S camera (or more properly, in a "non-mirror-box" camera) this shutter is a tiny "blinder" located adjacent to the iris (aperture) in the lens. It's so small, it can be very fast. It's so simple, it can be cheap. It makes almost no noise. A dSLR can be designed to ALSO have the shutter in each lens.

There are hundreds of lenses that would have to be redesigned, both mechanically and electronically (the little CPU in the lens would have to control the shutter)..

Guess what? There is considerable resistance to starting down that development path..

Now that we have that behind us, I think the fully electronic dSLR is coming. This is often called an "EVIL" camera. This name was coined by the status-quo industry to put a negative spin on these ideas. I bet you didn't know that you were "EVIL", did you?.

"EVIL" stands for "Electronic Viewfinder...Interchangeable Lens". This vision of high-level, pro-grade cameras drops the mirror-box, the pentaprism, the screen, etc. It moves the sensor forward in the body, so that it almost touches the back of the lenses. This placement allows much less expensive lenses to be used...and these lenses can have stunning optical quality! Since the profits from dSLR camras comes mostly from lens sales, there is just a tad bit of resistance to go here..

Bottom line: When the mechanical shutter goes away, the mirror-box will go away too. There is significant cost associated with these assemblies. It's cheaper to do them electronically. And the associated lenses will be smaller/cheaper/better. So really...why doesn't this get any traction? Because of the cost associated with the EVF...that's why. We're waiting for high-resolution, fast frame rate LCDs to become affordable.



Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #8

Wow... that's complicated..

Chuxter wrote:.

Outwest wrote:.

Pentaxiantrooper wrote:...a shutter helps to protect the sensor from.

Dust, otherwise you would have to put an airtight seal around themirror to avoid picking up dust during lens swaps..

Ok, now that makes sense..

No, it doesn't. The shutter is NOT airtight. Duh....

Here are the real reasons (it's a bit long, but often that's the casewith questions...they don't always have a one-line answer)..

The shutter in dSLRs do two things:.

1. Time the exposure..

2. Exclude light from the sensor during non-capture times (which isMOST of the time)..

The first one is the simpler of the two...let's start there. Yes, itwould be easy to substitute an electronic shutter. However, most dSLRsensors don't have that capability at this time. And there are smallissues with electronic shutters. There are many ways to do it. Thecheap ways have problems.

Most P&S cameras have a rolling shutter. Quality concious dSLRbuyers will not like this method..

That leaves the more expensive "global" or "frame" shutter. It ismore expensive because it requires an additional transistor at eachphotosite. That may sound trivial, but if a normal CMOS photosite has2 transistors, that is a 50% increase in transistors. Even worse, itincreases the non-photosensitive area at each photosite by about 50%.That negatively impacts light-gathering capability and this increasesnoise. Then there is the patent position. Companies like Kodak have amassive patent portfolio.

Is simply waitinguntil these patents expire?.

The second reason re blocking light from the sensor is probably moregermaine..

ALL cameras, even P&S types, have a "shutter" to block light from thesensor. This is required because if light is continuously shining onthe sensor, all the data would have to be transferred SIMULTANEOUSLY.Most sensors transfer data serially. To keep the photosites fromcontinuing to accumulate photons, cameras close the shutter duringthe period when data is being transfered. A sensor with a "global"electronic shutter helps, but all Silicon areas that are un-maskedgenerate electrons when photons hit them. These "free" electrons candecrease the signal-to-noise ratio..

SO, for several reasons, manufacturers must have a shutter. In a P&Scamera (or more properly, in a "non-mirror-box" camera) this shutteris a tiny "blinder" located adjacent to the iris (aperture) in thelens. It's so small, it can be very fast. It's so simple, it can becheap. It makes almost no noise. A dSLR can be designed to ALSO havethe shutter in each lens.

There are hundreds of lenses that would have to beredesigned, both mechanically and electronically (the little CPU inthe lens would have to control the shutter)..

Guess what? There is considerable resistance to starting down thatdevelopment path..

Now that we have that behind us, I think the fully electronic dSLR iscoming. This is often called an "EVIL" camera. This name was coinedby the status-quo industry to put a negative spin on these ideas. Ibet you didn't know that you were "EVIL", did you?.

"EVIL" stands for "Electronic Viewfinder...Interchangeable Lens".This vision of high-level, pro-grade cameras drops the mirror-box,the pentaprism, the screen, etc. It moves the sensor forward in thebody, so that it almost touches the back of the lenses. Thisplacement allows much less expensive lenses to be used...and theselenses can have stunning optical quality! Since the profits from dSLRcamras comes mostly from lens sales, there is just a tad bit ofresistance to go here..

Bottom line: When the mechanical shutter goes away, the mirror-boxwill go away too. There is significant cost associated with theseassemblies. It's cheaper to do them electronically. And theassociated lenses will be smaller/cheaper/better. So really...whydoesn't this get any traction? Because of the cost associated withthe EVF...that's why. We're waiting for high-resolution, fast framerate LCDs to become affordable.



Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/.

No hesitation when capturing moments..

Helping other is doing good for yourself, and treating the earth a little better will help the next generation.http://moments.zenfolio.com..

Comment #9

My quick answer,.

Most (and we know which ones don't we) DSLR cameras were build on older designs for film cameras, so they have shutters just like the film cameras. Someone has already said that when someone figures out a better way, someone will forge ahead and claim the credit for furthering the design...

Comment #10

Stainedsilver wrote:.

My quick answer,.

Most (and we know which ones don't we) DSLR cameras were build onolder designs for film cameras, so they have shutters just like thefilm cameras..

The second part of this statement simply doesn't follow from the first. It's nonsense...

Comment #11

Chuxter wrote:.

No, it doesn't. The shutter is NOT airtight. Duh....

The shutter doesn't have to be AIRTIGHT in order to offer some dust protection. If the shutter prevents some random dust from lodging on the sensor, then good..

Since the shutter is usually open for only fractions of a second, I can easily see how it would help keep dust off the sensor, especially during lens changes, etc..

Http://www.pbase.com/digirob..

Comment #12

Digirob wrote:.

Chuxter wrote:.

No, it doesn't. The shutter is NOT airtight. Duh....

The shutter doesn't have to be AIRTIGHT in order to offer some dustprotection. If the shutter prevents some random dust from lodging onthe sensor, then good..

Since the shutter is usually open for only fractions of a second, Ican easily see how it would help keep dust off the sensor, especiallyduring lens changes, etc..

You are right. But you failed to quote what I was objecting to. That apparently signals that I failed to communicate clearly and you didn't understand my comment. PT was suggesting that it was necessary that the mirror have an airtight seal around it to keep dust out if the shutter was not performing that function. I was simply commenting that the shutter wasn't airtight. I was not saying that the shutter didn't offer SOME dust protection during lens changes..

Here is the text (pentaxiantrooper) I was commenting about:.

"...and a shutter helps to protect the sensor from dust, otherwise you would have to put an airtight seal around the mirror to avoid picking up dust during lens swaps.".

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #13

Chuxter wrote:.

You are right. But you failed to quote what I was objecting to. Thatapparently signals that I failed to communicate clearly and youdidn't understand my comment. PT was suggesting that it was necessarythat the mirror have an airtight seal around it to keep dust out ifthe shutter was not performing that function. I was simply commentingthat the shutter wasn't airtight. I was not saying that the shutterdidn't offer SOME dust protection during lens changes..

On a more careful re-read, I could have interpreted it either way. Apparently I chose the wrong way. Just shows how easy it is to be misunderstood on these forums..

Http://www.pbase.com/digirob..

Comment #14

Digirob wrote:.

Chuxter wrote:.

You are right. But you failed to quote what I was objecting to. Thatapparently signals that I failed to communicate clearly and youdidn't understand my comment. PT was suggesting that it was necessarythat the mirror have an airtight seal around it to keep dust out ifthe shutter was not performing that function. I was simply commentingthat the shutter wasn't airtight. I was not saying that the shutterdidn't offer SOME dust protection during lens changes..

On a more careful re-read, I could have interpreted it either way.Apparently I chose the wrong way. Just shows how easy it is to bemisunderstood on these forums..

Yes..

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #15

Missing from this discussion (Maybe it was discussed in the five lost days) is any suggestion as to the advantages of a mechanical shutter..

Many cheaper SLRs have a combined mechanical and electronic shutter but more expensive DSLRs have a purely mechanical shutter. Why?.

First a brief description of the combined mechanical and electronic shutter. If light was able to hit the CCD/CMOS sensor at all times it would degrade over time. Further with an interchangeable lens camera there are obvious risks if the CCD were to be left exposed to the elements dust etc etc. So there has to be something to cover the CCD. With cheaper DSLRs the mechanical shutter handles speeds up to something like 1/90th of a second but thereafter further reduction of exposure time is achieved by electronic CCD gating..

The disadvantage of that system is that you can get blooming in certain light conditions. Take look at the photos mid page on this review comparing the Nikon D70 and D80:.

Http://www.imaging-resource.com/PRODS/D80/D80A5.HTM.

Put simply strong light overflows from full pixels to adjoining pixels on the CCD with the results you can see in the link above..

An unfortunate side effect of moving to a purely mechanical shutter is that the flash synch speed usually falls from 1/500th to 1/200th. (I am not sure why but that is a topic for another thread)..

Hope that helps.

Chris Elliott.

*Nikon* D Eighty + Fifty - Other equipment in Profile.

Http://PlacidoD.Zenfolio.com/..

Comment #16

Chris Elliott wrote:.

If light was able to hit the CCD/CMOS sensor at all times itwould degrade over time..

Doesn't the mirror reflect essentially all the light coming through any lens?.

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #17

Chris Elliott wrote:.

An unfortunate side effect of moving to a purely mechanical shutteris that the flash synch speed usually falls from 1/500th to 1/200th..

If it is like film, a focal plane shutter is only full sensor at a specific speed. Any speed faster than that the whole sensor is not exposed. But the flash has already thrown all it's light..

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Anandahttp://spaces.live.com/anandasimhttp://picasaweb.google.com/AnandaSimhttp://www.flickr.com/photos/32554587@N00/..

Comment #18

Chris Elliott wrote:.

With cheaper DSLRs the mechanical shutter handles speeds up tosomething like 1/90th of a second but thereafter further reduction ofexposure time is achieved by electronic CCD gating..

The disadvantage of that system is that you can get blooming incertain light conditions. Take look at the photos mid page on thisreview comparing the Nikon D70 and D80:.

Http://www.imaging-resource.com/PRODS/D80/D80A5.HTM.

Put simply strong light overflows from full pixels to adjoiningpixels on the CCD with the results you can see in the link above..

An unfortunate side effect of moving to a purely mechanical shutteris that the flash synch speed usually falls from 1/500th to 1/200th..

Interesting comparison, I haven't seen that before. I don't remember Ken Rockwell mentioning it when he was obsessing about 1/500 sync speeds ..

Comment #19

Steve Balcombe wrote:.

Chris Elliott wrote:.

With cheaper DSLRs the mechanical shutter handles speeds up tosomething like 1/90th of a second but thereafter further reduction ofexposure time is achieved by electronic CCD gating..

The disadvantage of that system is that you can get blooming incertain light conditions. Take look at the photos mid page on thisreview comparing the Nikon D70 and D80:.

Http://www.imaging-resource.com/PRODS/D80/D80A5.HTM.

Put simply strong light overflows from full pixels to adjoiningpixels on the CCD with the results you can see in the link above..

An unfortunate side effect of moving to a purely mechanical shutteris that the flash synch speed usually falls from 1/500th to 1/200th..

Interesting comparison, I haven't seen that before. I don't rememberKen Rockwell mentioning it when he was obsessing about 1/500 syncspeeds .

Not to start a flame fest but Rockwell isn't the best writer...

Comment #20

Mrxdimension wrote:.

Not to start a flame fest but Rockwell isn't the best writer..

That is a mild understatement!.

Chris Elliott.

*Nikon* D Eighty + Fifty - Other equipment in Profile.

Http://PlacidoD.Zenfolio.com/..

Comment #21

He's a great writer. Excellent, in fact. What he is not is a great photographer..

He probably didn't mention blooming because it's a non-issue...

Comment #22

Perhaps one can say he is not the most authoratative of writers..

As I have said more than once before he writes by the yard. - Never mind the quality feel the width!.

Chris Elliott.

*Nikon* D Eighty + Fifty - Other equipment in Profile.

Http://PlacidoD.Zenfolio.com/..

Comment #23

Electronic shutters are notorious for shutter lag and the G2 is a great example of what I am talking about. Try taking a picture of a moving child with a G2. Good luck..

Another issue with electronic shutters is depth of field which is controlled by the shutter and not mechanical. A DSLR has a mechanical iris in the lens that controls the light hitting the sensor just like a film camera and depending on the lens you get varying degrees of bokeh. The larger the size of the iris opening the greater the bokeh and the depth of field is very thin. G2's do not have an iris controlling the amount of light hitting the sensor and a pitcure taken at 1/250 sec at f/2.8 has the same bokeh if it was taken at f/16..

Bokeh is the out of focus part of the image. The better the Bokeh the smoother it looks..

Bill.

Shoot liberally!..

Comment #24

No, electronic shutters do not cause the lag. The lag comes from the autofocus mechanism..

Check the site 'imageing-resource' for timing on newer cameras from Fuji, Sony, Panasonic, Ricoh and Casio. All of these have a pre-focussed delay of less than 0.02 seconds..

Also, these cameras use a leaf type iris system in the lens to control the aperture. This is also quite fast and so does not contribute significantly to lag. If you have a camera with manual focus feature like the Fuji S6500 you can get very low shutter lag by presetting manually or by using pre-focus..

Cheers..

Comment #25

Wm Karoly wrote:.

Electronic shutters are notorious for shutter lag and the G2 is agreat example of what I am talking about. Try taking a picture of amoving child with a G2. Good luck..

Electronic shutters are not the cause of shutter lag - in fact they can actually be faster than mechanical shutters. But that's of academic interest only, because the G2 has a mechanical shutter..

Another issue with electronic shutters is depth of field which iscontrolled by the shutter and not mechanical..

No, that's wrong, but I'm not certain what you mean. In the G2, there is just one diaphragm which controls both aperture and shutter, so in that sense the 'shutter' controls depth of field. But is is mechanical..

A DSLR has a mechanicaliris in the lens that controls the light hitting the sensor just likea film camera and depending on the lens you get varying degrees ofbokeh. The larger the size of the iris opening the greater the bokehand the depth of field is very thin..

That part is right.

G2's do not have an iriscontrolling the amount of light hitting the sensor and a pitcuretaken at 1/250 sec at f/2.8 has the same bokeh if it was taken atf/16..

... but that is completely wrong. The G2 has a combined shutter/iris diaphragm which is normally closed - unlike a DSLR iris which is normally wide open. When the G2 shutter is fired, the diaphragm opens to the prescribed aperture for the duration of the exposure then closes again. By contrast, when a DSLR shutter is fired the (separate) aperture diaphragm narrows to the prescribed aperture then the shutter opens. But although the mechanism is different, the situation during the exposure is exactly the same - an iris diaphragm open at the specified aperture..

The depth of field and out-of-focus blur of a G2 are completely normal. See the example pictures here: http://www.dpreview.com/reviews/canong2/page13.asp - about 3/4 of the way down, headed "Aperture Priority Mode"...

Comment #26

Chuxter wrote:.

"EVIL" stands for "Electronic Viewfinder...Interchangeable Lens".This vision of high-level, pro-grade cameras drops the mirror-box,the pentaprism, the screen, etc. It moves the sensor forward in thebody, so that it almost touches the back of the lenses. Thisplacement allows much less expensive lenses to be used...and theselenses can have stunning optical quality!.

Would this really make *that* much difference in lens prices? Enough to eliminate all expensive lenses? A large portion of the cost of expensive lenses is the build quality so that the lenses will stand up to the rigors of professional use. How will moving the back portion closer to the sensor reduce build quality costs?.

I remember when Canon came out with their EF-S mount, that people promised that there would be cheaper, lighter, better lenses. This hasn't quite happened. At least not the cheaper part..

Does moving the back portion of the lens closer to the sensor help the design of all lenses? Or just wide angle?.

Since the profits from dSLRcamras comes mostly from lens sales, there is just a tad bit ofresistance to go here..

On the other hand, I don't think they'd dislike a situation where everybody would need to start out from scratch and buy a complete set of new lenses..

Wayne..

Comment #27

Let me start by saying that I too found massive problems with Bill's post. I find that few people know what is going on INSIDE a digital camera. They often create fantastic versions of reality, totally w/o any evidence that it is true..

I don't have a G2...I've never even seen a G2. I assume Bill has/had one? But I doubt that it works like he imagines....

Steve Balcombe wrote:.

Wm Karoly wrote:.

Electronic shutters are notorious for shutter lag and the G2 is agreat example of what I am talking about. Try taking a picture of amoving child with a G2. Good luck..

The G2 was introduced in the summer of '01...that's 6 and 1/2 years ago. To use it as an example/benchmark for non-mirror-box cameras seems out of place..

Electronic shutters are not the cause of shutter lag - in fact theycan actually be faster than mechanical shutters. But that's ofacademic interest only, because the G2 has a mechanical shutter..

Are you sure the G2 has a mechanical shutter that is used to time the exposures? I really don't know, but other cameras of that era didn't..

Another issue with electronic shutters is depth of field which iscontrolled by the shutter and not mechanical..

No, that's wrong, but I'm not certain what you mean. In the G2, thereis just one diaphragm which controls both aperture and shutter, so inthat sense the 'shutter' controls depth of field. But is ismechanical..

Hmmm....

A DSLR has a mechanicaliris in the lens that controls the light hitting the sensor just likea film camera and depending on the lens you get varying degrees ofbokeh. The larger the size of the iris opening the greater the bokehand the depth of field is very thin..

That part is right.

G2's do not have an iriscontrolling the amount of light hitting the sensor and a pitcuretaken at 1/250 sec at f/2.8 has the same bokeh if it was taken atf/16..

... but that is completely wrong. The G2 has a combined shutter/irisdiaphragm which is normally closed - unlike a DSLR iris which isnormally wide open. When the G2 shutter is fired, the diaphragm opensto the prescribed aperture for the duration of the exposure thencloses again. By contrast, when a DSLR shutter is fired the(separate) aperture diaphragm narrows to the prescribed aperture thenthe shutter opens. But although the mechanism is different, thesituation during the exposure is exactly the same - an iris diaphragmopen at the specified aperture..

If the G2 has an iris/shutter that is normally closed, how does the sensor see the image to be sent to the LCD?.

The other cameras of that era that I have examined have a separate "shutter", located just behind the iris. It IS possible to use the iris as a shutter, but they use a separate, single-blade "shutter" because it's faster and more reliable. But these "shutters" are NOT used to time the exposure. That is done electronically. The "shutter" is just used to remove the image from the sensor during the time picture data is accessed. This is necessary because the sensor continues to be photo-active..

The depth of field and out-of-focus blur of a G2 are completelynormal. See the example pictures here:http://www.dpreview.com/reviews/canong2/page13.asp - about 3/4 of theway down, headed "Aperture Priority Mode"..

I think Bill's opinion that the lens aperture doesn't affect DOF/bokeh is because the G2 has a small sensor and thus a short FL lens. Short FL lenses on ANY camera have wide DOF and yes, it's not affected as much by the aperture..

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #28

Wayne Larmon wrote:.

Chuxter wrote:.

"EVIL" stands for "Electronic Viewfinder...Interchangeable Lens".This vision of high-level, pro-grade cameras drops the mirror-box,the pentaprism, the screen, etc. It moves the sensor forward in thebody, so that it almost touches the back of the lenses. Thisplacement allows much less expensive lenses to be used...and theselenses can have stunning optical quality!.

Would this really make *that* much difference in lens prices? Enoughto eliminate all expensive lenses? A large portion of the cost ofexpensive lenses is the build quality so that the lenses will standup to the rigors of professional use. How will moving the backportion closer to the sensor reduce build quality costs?.

The build quality is an important issue. It has nothing to do with the optics issue. There are good optical lenses in poor physical mounts...most current 50mm f1.8 lenses seem to be examples of this..

SBF designs benefit mostly the wider FLs, but also the vastly popular zoom lenses that include WA ranges..

I remember when Canon came out with their EF-S mount, that peoplepromised that there would be cheaper, lighter, better lenses. Thishasn't quite happened. At least not the cheaper part..

Canon likes to make BIG profits? I don't know much about Canon....

Does moving the back portion of the lens closer to the sensor helpthe design of all lenses? Or just wide angle?.

See answer above..

Since the profits from dSLRcamras comes mostly from lens sales, there is just a tad bit ofresistance to go here..

On the other hand, I don't think they'd dislike a situation whereeverybody would need to start out from scratch and buy a complete setof new lenses..

Huh? The manufacturers would LOVE that. But WE would not. They know that..

EVIL prophets (like me) understand that issue. With just a little bit of creativity, we have proposed a solution: A rather simple adapter that extends legacy lenses forward a bit will allow them to be used. Something like this:.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Image control:Zoom outZoom 100%Zoom inExpand AllOpen in new window.

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #29

Chuxter wrote:.

I don't have a G2...I've never even seen a G2. I assume Bill has/hadone? But I doubt that it works like he imagines....

Nor me, but Bill's assertions didn't ring true so I looked at the Phil's review - that's where all my information comes from..

Http://www.dpreview.com/reviews/canong2/.

[snip].

Steve Balcombe wrote:.

... The G2 has a combined shutter/irisdiaphragm which is normally closed - unlike a DSLR iris which isnormally wide open. When the G2 shutter is fired, the diaphragm opensto the prescribed aperture for the duration of the exposure thencloses again. By contrast, when a DSLR shutter is fired the(separate) aperture diaphragm narrows to the prescribed aperture thenthe shutter opens. But although the mechanism is different, thesituation during the exposure is exactly the same - an iris diaphragmopen at the specified aperture..

If the G2 has an iris/shutter that is normally closed, how does thesensor see the image to be sent to the LCD?.

You're right of course - "normally" closed is wrong, I worded that badly. Closed at the beginning of the shutter cycle perhaps. (Or just read the review for Phil's description!).

The depth of field and out-of-focus blur of a G2 are completelynormal. See the example pictures here:http://www.dpreview.com/reviews/canong2/page13.asp - about 3/4 of theway down, headed "Aperture Priority Mode"..

I think Bill's opinion that the lens aperture doesn't affectDOF/bokeh is because the G2 has a small sensor and thus a short FLlens. Short FL lenses on ANY camera have wide DOF and yes, it's notaffected as much by the aperture..

Take a look at the quoted link above for a clear example...

Comment #30

Steve Balcombe wrote:.

Chuxter wrote:.

Steve Balcombe wrote:.

... The G2 has a combined shutter/irisdiaphragm which is normally closed - unlike a DSLR iris which isnormally wide open. When the G2 shutter is fired, the diaphragm opensto the prescribed aperture for the duration of the exposure thencloses again. By contrast, when a DSLR shutter is fired the(separate) aperture diaphragm narrows to the prescribed aperture thenthe shutter opens. But although the mechanism is different, thesituation during the exposure is exactly the same - an iris diaphragmopen at the specified aperture..

If the G2 has an iris/shutter that is normally closed, how does thesensor see the image to be sent to the LCD?.

You're right of course - "normally" closed is wrong, I worded thatbadly. Closed at the beginning of the shutter cycle perhaps. (Or justread the review for Phil's description!).

OK, I read Phil's description:.

"...it uses a single iris mechanism for both aperture and shutter. The iris opens at the beginning of the exposure to a certain size for the selected (or metered) aperture and then closes again at the end of the exposure. The speed at which the iris can go from a wide aperture (such as F2.0) to completely closed creates a limitation as to the maximum shutter speed available at different apertures.".

I'm sure that Phil is wrong and/or simply wrote it wrong, but I see where you got the bad info now...can't blame you. Let's take his description piece-by-piece....

1. I believe that it has a "single iris mechanism for both aperture and shutter" and that designing it that way produces the strange entanglement between aperture and shutter speed. That is EXACTLY why other cameras DON'T do it that way...it's simply too slow..

2. The iris DOES NOT open at the beginning of the exposure. It actually closes down from wide open to the selected aperture..

3. It does close at the end of the exposure, but it's not "closing again"...it's normally open (except when power is off or immediately after an exposure and stays closed during the time the CCD data is transfered)..

Unfortunately, although Phil is a smart guy, he isn't very knowledgable about the inner working of cameras. He's a computer nerd, after all...and came from an SLR background. And he's not alone in his confusion about these things..

It's relatively easy to see and hear what is going on...simply set a slow exposure time and look inside the lens and watch the iris and blade shutter (if there is one) operate. You can also make a digital recording of the SOUND of the iris and shutter operating to get an idea how the timing happens by using a sound editor..

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #31

Chuxter wrote:.

2. The iris DOES NOT open at the beginning of the exposure. Itactually closes down from wide open to the selected aperture..

3. It does close at the end of the exposure, but it's not "closingagain"...it's normally open.

That is completely at odds with the relationship between aperture and maximum shutter speed on the G2. The reason the maximum shutter speed is constrained at wider apertures (i.e. rather than smaller apertures) is that the diaphragm is opening up rather than stopping down..

Unfortunately, although Phil is a smart guy, he isn't veryknowledgable about the inner working of cameras. He's a computernerd, after all...and came from an SLR background..

You are so patronising Charlie. The whole point here is that the G1/G2 were unconventional - the inner workings of other cameras having nothing to do with it..

It's relatively easy to see and hear what is going on...simply set aslow exposure time and look inside the lens and watch the iris andblade shutter (if there is one) operate..

Easy for you to do, but too hard for the computer nerd who wrote the review? You are a very special person Charlie...

Comment #32

Steve Balcombe wrote:.

Chuxter wrote:.

2. The iris DOES NOT open at the beginning of the exposure. Itactually closes down from wide open to the selected aperture..

3. It does close at the end of the exposure, but it's not "closingagain"...it's normally open.

That is completely at odds with the relationship between aperture andmaximum shutter speed on the G2. The reason the maximum shutter speedis constrained at wider apertures (i.e. rather than smallerapertures) is that the diaphragm is opening up rather than stoppingdown..

Good point. I missed the direction of the effect..

Let's look at some obvious things....

1. The lens has to be open normally. If it was normally closed, the LCD would not show the scene..

2. If the lens is closed immediately prior to the exposure (as you and Phil say) then it must have just closed..

3. Then the timing relationships reported would work..

4. And the lens would close again after the exposure to insure darkness during data access..

The only mystery in this scenario is WHY it had to close BEFORE the exposure started?.

Unfortunately, although Phil is a smart guy, he isn't veryknowledgable about the inner working of cameras. He's a computernerd, after all...and came from an SLR background..

You are so patronising Charlie. The whole point here is that theG1/G2 were unconventional - the inner workings of other camerashaving nothing to do with it..

I wasn't aware that the G1/G2 were special. The review, at least in hindsight, doesn't make it SEEM special....

It's relatively easy to see and hear what is going on...simply set aslow exposure time and look inside the lens and watch the iris andblade shutter (if there is one) operate..

Easy for you to do, but too hard for the computer nerd who wrote thereview? You are a very special person Charlie..

OK, that may have been presumptious of me. But I watch what he does. I have been wishing Phil would report more of the inner workings for years. My guess has always been that he didn't know how to. He consistently rejects all suggestions that he (or somebody else) should develop an objective test of IS/VR...says it's not technically feasible. We suggest that he ask the various manufacturers how THEY verify that their IS/VR improves their cameras...and how they quantify exactly how MUCH it helps.

Now this may be more of a business choice...he may not want to open this bag of worms? We suggest he measure VF brightness. We ask for a quantitative measure of VF field of view. We want dSLRs to be tested with several AF lenses to correlate AF speed not just with the body, but to include the speed of the AF motor in the lens..

And last, it would be VERY interesting when there is a SPECIAL camera like the G1/G2 that does weird things, to dig deep into how and why it does these things..

Please don't interpret my "gripes" as failure to appreciate what Phil has done. But it APPEARS that he doesn't have the skills to do some of these things..

BTW, I think everybody is special... .

Charlie DavisNikon 5700, Sony R1, Nikon D300HomePage: http://www.1derful.infoBridge Blog: http://www.here-ugo.com/BridgeBlog/..

Comment #33

It's actually fairly easy to implement an electronic shutter on a sensor. However, like with any design process, certain features trade off against others..

Shutters serve two roles. One is to initiate the onset of an exposure and the other is to terminate it. An iris-type shutter uses the same mechanism to implement both roles: creating and then closing an opening. SLRs, on the other hand, use a two-curtain system. One curtain opens and a second closes to end the curtain. This arrangement allows for faster shutter speeds, although the actual exposure rolls across the surface of the sensor instead of happening simultaneously everywhere..

Consider the first curtain first. Initiating exposure for a given pixel or row of pixels is just a matter of holding the reset line for these pixels in the reset position, releasing the pixels to allow accumulation of charge in order to "open" the shutter. This is *already* implemented in several cameras, the 40D being one of them. Silent Mode 1 relies on this feature. The first curtain is open well in advance to allow the sensor to receive light for Live View mode. For exposure, the reset signal is released in a rolling fashion across the sensor, with the mechanical second curtain following behind after a delay to block further light and terminate the exposure..

So, this half is the problem is solved and in place..

The second half of the problem, that of terminating the exposure electronically, is also easy. This is especially true in a CCD where such products exist. You simply interleave columns of dummy pixels, covered in opaque material so as prevent the entry of light, in between the columns of normal, optically-active pixels. At the end of the exposure, all charge from each column of active pixels is transferred next door to the dummy pixels. Readout is then from the dummy pixels, which hold the charge constant until it can be read out..

Note the severe consequence of this design, however. Half the sensor area consists of dummy pixels, which serve merely to buffer the charge from their adjacent pixels. The sensor is therefore only half as sensitive and can accumulate only half the charge as one without these buffer pixels..

Since DSLRs sell partly on low noise, this is just too much of a tradeoff. Not that it isn't done. From the Nikon D70s high flash sync speed, this camera's sensor likely implements a second curtain electronic shutter. Note, however, that Nikon dropped this capability on subsequent cameras, probably because the pressure to reduce noise was greater than the call to keep a high sync speed..

David..

Comment #34

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